- Background. Streptococcus pyogenes, or group A (3-hemolytic Streptococcus (GAS), is an important causative agent of bacterial pharyngotonsillititis and skin, soft-tissue, and invasive infections. Although it is also an important pathogen in acute otitis media (AOM), its exact role has not been determined. Methods. Patients aged 0-18 years with AOM, from whom a specimen of middle-ear fluid was obtained and cultured during 1999-2003, were enrolled. Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and GAS were considered pathogens. Information collected included demographic characteristics, clinical history, and signs and symptoms. Results. GAS otitis was observed in 350 (3.1%) of 11,311 episodes (of which 117 were also culture-positive for other pathogens). The other 10,961 episodes involved H. influenzae only (n = 2507), S. pneumoniae only (n = 2131), dual infection with H. influenzae and S. pneumoniae (n = 1290), M. catarrhalis only (n = 129), and other combinations of pathogens (n = 271). Increased age and Jewish ethnicity were independent, significant, positive risk factors for GAS AOM, and fall season was a negative risk factor. Episodes of GAS infection were less frequently bilateral, febrile, and accompanied by other systemic findings than were other episodes of other types of infection. Most patients with GAS AOM presented with acute drainage from the ears. A lower proportion of cases of AOM were due to GAS in children with recurrent AOM and in patients recently treated with antibiotics, compared with patients with AOM who did not have these factors. The risk for mastoiditis was highest among patients with GAS AOM, compared with patients infected with other pathogens: 11.6 episodes per 1000 episodes of GAS AOM, compared with 2.2,0.3, and 0 episodes of mastoiditis per 1000 episodes of AOM due to S. pneumoniae, H. influenzae, and M. catarrhalis, respectively. Conclusion. Compared with AOM caused by pathogens other than GAS, GAS AOM is characterized by older age and higher local aggressiveness manifested by lower rates of fever and respiratory symptoms and higher rates of tympanic perforation and mastoiditis.